Modern, large volume commercial photographic laboratories process exposed photographic film in an automated assembly line environment. Usually, several rolls of exposed photographic film are spliced into a single continuous strip for development and printing. Efficient management of the automated photo processing environment requires correlation of each negative frame with each print, and with stored electronic data regarding each photographic subject.
To facilitate this correlation, it is now common practice to physically mark the edge of each individual photographic negative frame by punching one or more small holes in the film edge. In the simplest case, a single punched hole may be made in the film edge between exposures to designate the separation point between the two exposures. Such a mark may be detected by a suitable sensor as the film is transported through an automated printer, for example, to initiate a series of machine based instructions in the printer. In this fashion, the printer may use the signal generated by such a sensor to (1) advance the strip of film through the optical stage of the printer, (2) advance an associated roll of photographic paper, (3) illuminate an exposure lamp and (4) activate the printer shutter.
Under other circumstances, it is desirable to provide positive identification of each negative frame by providing each negative frame with a discrete identifying code. Using a hole punch, the edge of each frame of film can be encoded with a pattern of machine readable holes, e.g., in binary-coded decimal (BCD) format. This discrete identifying data is readily correlated to other data regarding each negative frame. This other data may take the form of a computer data record which is stored, sorted, retrieved, utilized and edited simultaneously with the processing of the film. An example: a photographer takes a photo of a series of human subjects as part of a single photographing job. Midway through the job, one of the subjects blinks his eyes just as the camera shutter is closed. The photographer makes a second exposure of that subject, and identifies the first exposure as a "blink", in his processing notes. If each negative frame can be positively identified by edge marking, the photographer can instruct the lab not to make prints of the "blink" frame. This information is commonly stored in a computer data base organized by frame identifier. The film edge punch code is easily correlated to the data base to provide automated control over many similar aspects of the photo processing activity.
A variety of methods for punching the film edge have been developed. The best devices currently known comprise a collection of small individual punch pins co-located in a unitary punch block. An associated die block contains a series of die openings adapted to receive the punch pins. The punch pins are spring biased and slidably mounted within the punch block by a plurality of pneumatic actuators. When any individual actuator extends, a plunger pushes on the associated pin. When the punch block and die block are forced together, each such extended pin protrudes from the punch block and into the die block. A film edge placed between the two blocks will be punched, accordingly, with a pattern of holes corresponding to the pattern of constrained pins.
As the punch and die blocks are separated, the pneumatic actuators also retract, allowing the pins in the punch block to return to the retracted position under the influence of the spring biasing means. Frequently, however, uneven pin wear characteristics, slugs generated from the punching process, or bias spring fatigue cause the pin to remain in the extended position, impeding the movement or removal of the photographic film from the die and punch blocks. This, in turn, impedes further movement of the film through the punching station.